This invention relates to conductive layers formed atop substrates, e.g., semiconductor structures.
In particular, it relates to a method for forming a layer, or layers, of metallization so that the insulating layer covering each layer of metal is substantially planar with respect to the substrate.
In the usual methods of forming thin film integrated semiconductor circuits containing passivating or insulating films over raised conductive line patterns on a substrate, the film ordinarily follows the contours of the underlying metallization pattern. The insulating layer has raised portions or elevations corresponding to the pattern. In structures having several such layers of metallurgy, the elevated portions formed by the conductive lines at the locations where insulation passes over or under the lines are a principal cause of pinholes and stress cracks in the insulation layer as well as pinholes in the metallization. Moreover, the effect is cumulative and increases with the number of metallurgical levels atop the semiconductor.
Copending application Ser. No. 103,250 of R. P. Auyang et al, filed Dec. 31, 1970, and assigned to the assignee of the present invention, relates to a method for solving this problem. In that application, the insulating layer is sputtered quartz and the invention is a novel method for removing all elevations from the deposited quartz by resputtering to completely planarize the surface of the layer. The Auyang et al., technique has been eminently successful. However, it is time consuming; and planarization by resputtering alone is limited by the width of the metallic land pattern.
Thus, it may take as much as 24 hours of R. F. resputtering to completely planarize a conventional quartz layer deposited over a raised metallization pattern having stripes of standard width, say 300 to 1500 microinches. In addition, for large line widths, R. F. resputtering may not completely planarize the layer effectively. As disclosed in the Auyang et al. application, the resputtering may then be supplemented by a conventional chemical etching step on extremely wide stripes. This adds to the number of process steps required, hence to the cost of manufacturing. In addition, the passivation and insulation properties of sputtered quartz are not as good as desired. Moreover, sputtering equipment is complicated and expensive.